Epidermis, cornification, keratinization Flashcards
What keratins are expressed by basal keratinocytes in dogs?
K5, K14, K1, K6 (5+14 are the main ones to know)
How many cells are included in the epidermal proliferative unit model of epidermal stem cell division?
10 cells (in basal layer)
What population of cells is unique to the epidermal proliferative unit?
Transit amplifying cells - these proliferate rapidly to produce terminally differentiating cells in the epidermis
Name the layers of the epidermis (deep to superficial)
Basale - spinosum - granulosum - corneum
What makes up the spines of the cells in the stratum spinosum?
Desmosomes
What proteins and keratins start to be produced in the spinous cell layer?
K1, K10, involucrin, profilaggrin
What are keratohyalin granules?
Accumulations of synthesized proteins and lipids needed for the SC (primarily profilaggrin, loricrin, KIF)
In what layer of the epidermis do the KIF begin to assemble?
Stratum granulosum
In what layer does construction of the cornified envelope begin?
Stratum granulosum
Where are the contents of lamellar granules released?
Interface between stratum granulosum and stratum corneum
What does the cornified cell envelope take the place of?
Plasma membrane
What type of filament of the epithelial cell cytoskeleton is the largest?
Microtubules (20 nm diameter)
What type of filament of the epithelial cell cytoskeleton is the smallest?
Microfilaments (7 nm diameter, composed of actin)
Describe the structure of keratin proteins
Central alpha-helical rod domain, amino-terminal head, and carboxy-terminal tail
What type of keratins are acidic?
Type I (K9-19)
What type of keratins are basic or neutral?
Type II (K1-8)
What protein binds KIFs, facilitating the flattening of cornified cells?
Filaggrin
What is the general term for filaggrin degradation products?
Natural moisturizing factors
What are the products of filaggrin degradation?
AAs
urocanic acid
pyrrolidone carboxylic acid
lactic acid
citrate
sugars
What enzyme is required for filaggrin degradation?
Caspase-14
An increase in which intracellular ion results in increased transglutaminase activity?
Calcium
What enzymes catalyze the formation of bonds which cross-link involucrin to other CE proteins?
Transglutaminases 1+3
What protein is the major structural component of the cornified envelope?
Loricrin (70% of CE mass)
What enzyme cross-links loricrin to small proline-rich peptides?
Transglutaminase 3
What enzyme cross-links the loricrin+proline-rich peptide oligomers to the CE?
Transglutaminase 1
What protein helps traffic lamellar granules from the Golgi network to the plasma membrane?
CHEVI complex
(C-homologues in endosome-vesicle interaction)
What is the primary signal that induces lamellar granule secretion between the granular and cornified layers?
Increased intracellular calcium
What converts glucosylceramides into ceramides in the intercellular lamellae?
beta-glucocerebrosidase
What are the breakdown products of phospholipids?
FFAs, glycerol
What is the function of glycerol in the SC?
hydration (hygroscopic molecule)
What is the function of FFAs in the SC?
acidification – important for enzyme functions (esp beta-glucocerebrosidase and acidic sphingomyelinase)
What is the breakdown product of sphingomyelin?
ceramides
What enzyme converts sphingomyelin into ceramides?
acidic sphingomyelinase
What are the major lipid classes in the SC?
ceramides (50% of lipid mass)
FFAs (25% of lipid mass)
cholesterol (15% of lipid mass)
What group of ceramides is unique to the SC?
omega-hydroxyceramides (ceramides 1, 4, 9)
What are omega-hydroxyceramides bonded to?
involucrin, envoplakin, periplakin (help make up the cornified lipid envelope)
What would be the clinical manifestation of a malformation of the cornified lipid envelope?
Ichthyosis
What two enzymes are the key rate limiting enzymes in FFA synthesis?
acetyl-CoA carboxylase, fatty acid synthase
What fatty acids are NOT synthesized by the epidermis?
omega-3+6 polyunsaturated EFAs (i.e. linoleic acid and alpha-linolenic acid)
What specific fatty acids must be supplied by the diet/topicals?
linoleic acid (omega 6 PUFA)
alpha-linolenic acid (omega 3 PUFA)
What is the rate-limiting enzyme in cholesterol synthesis?
hydroxymethylglutaryl CoA reductase (HMG CoA)
What are two possible outcomes that happen to cholesterol synthesized in the lower epidermis?
1) Some is incorporated into lamellar granules and secreted into SG-SC interface unchanged
2) Some is sulfurylated, diffuses across membrane, and is metabolized back to cholesterol
What enzyme converts cholesterol sulfate back to cholesterol
Steroid sulfatase
Where does steroid sulfatase come from?
Secreted by lamellar granules
What is the role of cholesterol sulfate?
Inhibits serine proteases involved in desquamation
What is the desmoglea?
Extracellular part of desmosomes between adhered keratinocytes
Which desmosome plaque is intertwined with KIFs?
Inner dense plaque
What desmosome plaque borders the plasma membrane?
Outer dense plaque
What proteins are the transmembrane molecules that form an adhesive interface between neighboring keratinocytes?
Cadherins
What cadherins comprise the desmoglea?
Desmogleins
Desmocollins
What protein family binds to the cytoplasmic portion of cadherins?
Armadillo proteins (Plakoglobin, plakophilin)
What protein binds desmoplakin and cadherins?
Plakoglobin
What protein facilitates lateral linkage between desmoplakins?
Plakophilin
What protein binds KIFs to plakoglobin?
Desmoplakin
What do corneodesmosomes contain?
Desmoglein 1, desmocollin 1, corneodesmosin
What proteins in the epidermis are known to have glycine loops?
Keratins, loricrin, corneodesmosin
What is the function of glycine loops?
Mediate reversible and adjustable adhesion (acts like Velcro not glue)
Where is corneodesmosin synthesized?
In the granular keratinocyte
Where is corneodesmosin secreted?
Into the intercellular space starting in the SECOND layer of the SG
What protein is progressively cleaved as corneocytes advance towards desquamation?
Corneodesmosin
How does corneodesmosome distribution differ between lower and upper SC?
Lower SC: corneodesmosomes are all around the KC surface
Superficial SC: corneodesmosomes are only at periphery of KC
What is responsible for the superficial basket-weave of the layers of the upper SC?
Corneodesmosome distribution limited to periphery of cells in the upper SC
(deeper SC appears more compact microscopically because corneodesmosomes are all around the KC)
What transmembrane molecules make up epidermal tight junctions?
Claudins
Occludins
Which claudins are expressed in the epidermis?
Claudins 1, 4, 7
Which intracellular proteins help make up epidermal tight junctions?
zonula occludens proteins
Where are adherens junctions found on basal cells?
Lateral and apical membranes
Where are adherens junctions found on suprabasal cells?
entire cell surface
What junction links the actin cytoskeleton to the plasma membrane?
Adherens junctions
What protein classes are involved in adherens junctions?
Cadherins and catenins
How long does it take for complete renewal of the human epidermis?
28 days
What 2 protein classes are involved in desquamation?
kallikreins
Cathepsins
What proteins are cleaved by KLK5?
Corneodesmosin
Desmoglein 1
Desmocollin 1
What proteins are cleaved by KLK7?
Corneodesmosin
Desmocollin 1
Which KLK are involved in degrading corneodesmosomes?
KLK 1, 5, 6, 7, 14
Which KLK degrade desmoglein 1?
KLK 1, 5, 6, 14
What proteins cleave corneodesmosin?
KLK 5
Cathepsin L-like enzyme
Cathepsin D
What is the concentration of Ca2+ in the lower epidermis as compared to the upper epidermis?
Low in SB and SS, increased in SG, decreased again in SC
What structures provide a barrier to water loss in non-cornified epidermis?
Tight junctions
What structures regulate the Ca2+ gradient in the epidermis?
Tight junctions and the SC